1. Field of the Invention
The present invention relates to an optical recording/reproducing apparatus for recording/reproducing data using an optical recording medium such as an optical card.
2. Description of the Related Art
In recent years, a technique of data processing has been developed, and media for recording a large amount of data have been required. As one of the media, an optical recording medium has received a great deal of attention. An optical card is known as one of the optical recording media. As an apparatus for recording data onto the optical card and reproducing data of the optical card, an optical card recording/reproducing apparatus is practically used.
In the optical card, a laser beam is radiated through a lens on a data recording layer having a high reflectance and arranged on a substrate having the same shape as that of a credit card to form pits (holes) having a low reflectance on the recording layer by a thermally irreversible change, thereby writing data on the recording layer. The optical card has a recording capacity several or ten thousand times that of a conventionally used magnetic card. Although data cannot be rewritten in the optical card as in an optical disk, the recording capacity of the optical card is very large, i.e., 1 to 2 MG. Therefore, optical cards can be used in a variety of applications such as bankbooks, portable maps, prepaid cards used in shopping or the like. In addition, since the optical card has the characteristic feature of inhibiting data rewrite, the optical card can be used in applications such as individual health management cards which does not allow illegal data updating.
FIG. 1 is a plan view showing an optical card. An optical data recording portion 4 having a plurality of parallel tracks 4a is formed on an optical card 2 in a lateral direction. Data is recorded on the tracks 4a by forming data pits and data is reproduced from the tracks 4a by reading the data pits. Forming/reading data pits is performed by scanning a light beam emitted from an optical head in a direction along the tracks 4a. Scanning is usually performed by reciprocally moving the card 2 in a direction along the tracks 4a. Therefore, the data pits may be read in a direction reverse to the direction in which the data pits are formed. In order to correctly read the data, reproduced data is temporarily written in a buffer memory, and a data string is inverted in a direction of the time axis in accordance with the reproduction direction.
ID portions 6a and 6b in which identification data such as track addresses are recorded are formed on both ends of the data recording portion 4. Although the tracks 4a are formed to extend over the entire length of the optical card 2, the end portions of the tracks are easily damaged or contaminated and have poor reliability. Further, in order to sufficiently stabilize a relative moving speed between the optical card and the optical head in the track directions, the ID portions 6a and 6b are formed at positions inward from the ends of the card at predetermined distances (e.g., 4 mm). A data recording portion 8 is defined between the ID portions 6a and 6b. Since data are read from both the directions of the optical card while the optical card is reciprocally conveyed, the ID portions 6a and 6b are formed so that track addresses can be read from both directions. Therefore, in FIG. 1, when a light beam is moved from the left to the right along the tracks, the left ID portion 6a is read; when a light beam is moved from the right to the left, the right ID portion 6b is read, thereby identifying a tracking address. Thus, the ID data such as the tracking address can be read out regardless of a scanning direction before data is read out.
An optical system of the optical head for reproducing data of the optical card is shown in FIG. 3. A laser beam emitted from a light-emitting element 4' such as a laser diode is collimated into a parallel beam by a collimator lens 5, diffracted by a diffraction grating 6', and focused on the optical card 2 through an objective lens 7. The focused light is reflected by the optical card 2, and is incident on a detector 10 through a mirror 8' and a detection system lens 9.
The focused light beam on the optical card 2, as shown in FIG. 2, is constituted by a 0th-order diffracted beam 601 called a main beam and two 1st-order diffracted beams 602 and 603 called sub-beams, all of which are diffracted by the diffraction grating 6'. The main beam 601 is used to reproduce the data pits 203 or to generate a focus error signal for focusing control, and each of the sub-beams 602 and 603 is radiated half on a corresponding one of the track guides 201 and is used to generate a tracking error signal.
The light beam reflected by the optical card 2 and incident on the detector 10, as shown in FIG. 4, is constituted by three beams. Light beams 101, 102, and 103 shown in FIG. 4 correspond to light beams 601, 602, and 603 shown in FIG. 2, respectively. In the detector 10, an optical system is constituted such that the light beam 101 is radiated on the dividing line of detection regions 101a and 101b obtained by dividing a square detection region, the light beam 102 is radiated on the center of a detection region 102a, and the light beam 103 is radiated on the center of a detection region 106a.
In addition, the optical system is constituted such that the light beam 101 is moved in the direction perpendicular to the dividing line of the detection regions 101a and 101b when the beam on the optical card is defocused. Therefore, when a difference between amounts of light incident on the detection regions 101a and 101b is calculated, a focus error signal representing an error of the in-focus position can be obtained. When the objective lens 7 is driven by a driving means 11 according to the focus error signal to be brought close to or separated from the card 1, focusing control is performed such that the light beam is kept in an in-focus state on the card.
When the beams 602 and 603 shown in FIG. 2 are moved in the direction perpendicular to the tracks 202, the overlapping areas of the beams 602 and 603 on the track guides 201 are changed. Therefore, tracking error signals representing errors of the beams 602 and 603 from the centers of the track guides 201 can be obtained by calculating an output difference between the detection regions 102a and 106a. The objective lens 7 is moved by the driving means 11 in the direction perpendicular to the track guides 201 according to the tracking error signal, so that tracking control is performed to keep the beam 601 at the center of each of the tracks 202.
FIG. 5 is a view for explaining an access method of an arbitrary track, which method is employed in the optical data recording/reproducing apparatus arranged as described above.
In FIG. 5, as in FIGS. 2 and 4, reference numerals 201 denote track guides for guiding the light beam in the track directions; 202, tracks formed between the track guides 201; 601, a main beam for reproducing data pits formed along the tracks 202 and for generating focus error signals; and 602 and 603, sub-beams, each formed to half overlap a corresponding one of the track guides 201, for generating tracking error signals. In FIG. 5, both the ends of the tracks 202 represent both the ends of the card, arrows a, b, c, and d indicate the moving direction of the beam on the card. In general, the beam is moved on the card in a direction a or c perpendicular to the tracks by moving an optical head itself or an objective lens, and the beams on the card are moved in a direction b or d parallel to the tracks by moving the card with respect to the optical head.
Data reproduction of a given track is designated by an external apparatus (not shown) such as a host computer. This given track designated by a reproduction request is referred to as a target track address. In the example of FIG. 5, the target address is represented by AD1. A light beam is moved in the direction of an arrow a by a difference between a track address A0 at which the main beam 601 is currently located and the target track address AD1. Data of the target track AD1 is read by scanning the light beam (by moving the optical card) in the track direction of an arrow b. When the light beam reaches the right end of the track AD1, the light beam is moved in the direction of an arrow c by one track. Data of the next track AD2 is read by scanning the light beam (by moving the optical card) in the track direction of an arrow d. When the light beam reaches the left end of the track AD2, the light beam is moved in the direction of an arrow e by one track. Data of the subsequent tracks are read by scanning the light beam in the same manner as above. The above scanning is sequentially repeated until the number of read tracks reaches N.
According to the above data read operation, a total of N track scannings must be respectively performed so that a long time is required for a reproduction operation, and the reproduction operation cannot be performed at very high speed.
The drawback of the above access method is also applicable to the recording operation.